If the farmer got them from a 2000 year old tomb, then that makes him a graverobber, and an archeological looter. There is now no way to know how or where these pearls are from, since they were not scientifically excavated. From that standpoint, it makes them worthless, because there is no proof of where they came from. If you have them evaluated by a gemology lab, they can only tell you if they are possibly natural pearls and maybe what kind of mollusk created them.